In recent years, as a battery anticipated to have a small size, a light weight and high capacity, a non-aqueous electrolytic solution-based secondary battery such as a lithium ion battery has been proposed and put into practical use.
The lithium ion battery is configured to have a cathode and an anode which have properties capable of reversibly intercalating and deintercalating lithium ions, and a non-aqueous electrolyte.
Regarding an anode material for the lithium ion battery, as an anode active material, a carbon-based material or a lithium-containing metal oxide having properties capable of reversibly intercalating and deintercalating lithium ions such as lithium titanate (Li4Ti5O12) is generally used.
On the other hand, as a cathode material of the lithium ion battery, an electrode material mixture is used which includes, as a cathode active material, a lithium-containing metal oxide having properties capable of reversibly intercalating and deintercalating lithium ions such as lithium iron phosphate (LiFePO4), a binder and the like. Then, the electrode material mixture is applied to the surface of a metal foil which is called a collector to form the cathode of the lithium ion battery.
Compared with conventional secondary batteries such as lead batteries, nickel-cadmium batteries and nickel-hydrogen batteries, the lithium ion batteries have a lighter weight, a smaller size and higher energy. Therefore, the lithium ion batteries are used not only as small-size power supplies in portable electronic devices such as mobile phones and notebook personal computers but also as large-size stationary emergency power supplies.
In addition, recently, studies have been performed regarding the use of lithium ion batteries as high-output power supplies for plug-in hybrid vehicles, hybrid vehicles and electric power tools, and such batteries used as the high-output power supplies are required to have high-speed charge and discharge characteristics.
However, electrode active materials, for example, electrode materials including a lithium phosphate compound having properties capable of reversibly intercalating and deintercalating lithium ions have a problem of low electron conductivity. Therefore, as an electrode material having increased electron conductivity, there have been proposed electrode materials in which the particle surfaces of an electrode active material are uniformly coated with a chemically accumulated carbonaceous film to improve the current density of the electrode active material (for example, refer to Patent Documents 1 to 5) and the like.